Wolfgang Amadeus Mozart actually wrote his stylistically pace-setting Clarinet Quintet K. 581 for an instrument that has become known as the "basset clarinet," and which had four semitones more than the A clarinet in its lower register. The man who commissioned the piece, Mozart’s friend the clarinet virtuoso Anton Stadler, had had this instrument made specifically for him, so that he was the only one able to perform the work at first. After Mozart’s death, however, the work was soon published in the well-known A clarinet version. In his new edition, Werner Breig is faithful to the source of this work which, unfortunately, has only been transmitted as an arrangement. In his reconstruction, he attempts to come as close as possible to the original version for basset clarinet, which is no longer extant. The discrepancies between the two types of clarinets are distinguished through ossia variants in the score. The set of parts contains an additional, separate part for the basset clarinet, an instrument that can be found again today in historically accurate modern-day versions.